The background of the present invention comprises the art of rigid disk files, the art of magnetic recording media lubrication, and the art of thin film magnetic recording media.
In the art of rigid disk files it is known that one or more disks are supported for rotation on a motor-driven spindle. These disks cooperate with a movable read/write magnetic head assembly. The heads of this assembly fly close to the disks' recording surface, usually no more than 15 microinches above the disk surface. It is preferred that the disk file includes a sealed, or a substantially sealed external housing or container. U.S. Pat. No. 4,556,969 is an example of a disk file having a sealed container.
It is known that high speed rotation of the above mentioned motor-driven spindle creates a low pressure zone within the disk file enclosure. When the enclosure is not sealed, this low pressure zone can be used to induce the flow of filtered air into, through, and out of the enclosure. U.S. Pat. No. 4,471,395 is exemplary and is incorporated herein by reference.
It is known that the disk recording surface should preferable include a film of lubricant. In the art of magnetic media lubrication, it is known that saturated fatty acids, such as palmitic acid and stearic acid, are preferred lubricants. U.S. Pat. Nos. 4,526,833 and 4,539,266 are examples.
U.S. Pat. No. 4,626,941 describes a sealed disk file wherein the disks' recording surfaces are lubricated. The teaching of this patent deals with suppressing evaporation of the lubricant. This patent locates a lubricant source and a number of lubricated disks inside an air-tight enclosure. The lubricant source is exposed to the flow of hot air that is produced by rotation of the disks. As a result, the enclosure is filled with lubricant vapors. This environment of vapor-rich air suppresses evaporation of lubricant from the surface of the disks.
The construction and arrangement of this patent suppresses evaporation of the disks' lubricant film by "filling up" the inside space of the air-tight enclosure with lubricant vapor. The patent specifically teaches that the temperature of the lubricant source should be "as high as possible" and that the selected lubricant should have the "highest evaporation rate". This produces a vapor-rich environment for the disks. Because of this vapor-rich environment, the lubricant film thickness is inherently thick, as compared to the thin 3 to 15 angstrom film of the present invention. Specific examples "as small as 100 angstroms" and 70 angstroms are described in the referenced patent.
As will be apparent, the teachings of the present invention utilize Langmuir kinetics to maintain a thin mono-molecular organic lubricant layer or film on magnetic recording media in the form of disks. These disks include a recording surface having an affinity for organic molecules.
The present invention requires that the construction and arrangement of U.S. Pat. No. 4,626,941 be avoided. More specifically, the present invention teaches that in order to maintain a mono-molecular lubricant film on the disks, bulk transfer of lubricant to the disks, as by distillative or sublimative transfer of lubricant molecules, must be prevented.
As will be appreciated by those of skill in the art, the thickness of the lubricant film in the referenced patent is in the range of at least 70 to 100 angstroms, which provides a layer on top of the recording layer that is an appreciable percentage of the surface roughness of thin-film magnetic disks. The present invention establishes a lubricant film in the range of only 3 to 15 angstroms. This much thinner lubricant layer is a smaller percentage of the disk's surface roughness. As is well known, excessive lubricant (or any organic material) can dramatically increase the coefficient of friction between the heads and magnetic disks, which if too severe will cause the file to become stuck.
In the art of thin film magnetic recording disks, it is known that a sputtered carbon film or overcoat layer, on the disk's recording surface, improves the mechanical durability of the head-to-disk interface. It is also known that this interface is preferably lubricated. U.S. Pat. No. 4,529,651 is an example of a means for forming a protective coating on a magnetic recording layer by means of a sputtering technique.
It is known that the vapor pressure of a material, such as a lubricant, is a function of the material's molecular structure and of the material's temperature. Generally, solids have a lower vapor pressure than do liquids. The vapor pressure of solids varies greatly, depending upon the material.
The vapor pressure of palmitic acid and stearic acid, exemplary lubricants usable in the present invention, are both considerably less than one atmosphere. More specifically, the temperature at which the vapor pressure of palmitic acid is 1 mm of mercury is about 153.6.degree. centigrade, and the temperature at which the vapor pressure of stearic acid is 1 mm of mercury is about 173.7.degree. centigrade.